Fire Science And Fire Protection System Performance

The fire protection system can be divide into three fire fighting philosophies: Fire suppression, Fire extinguishment, Fire control.

Fire control

Limiting the fire’s size by distributing the water to decrease the heat and prevent a fire from spreading very rapidly across a gap because of intense heat (Flashover), which the sprinkler systems do to cool the fire before it reaches the flashover point.

Fire Extinguishment

Discharging of the fire suppression system ensures no combustion after the fire event.

Fire Suppression

The sharp reduction of the rate of heat release of a fire and the prevention of regrowth.

THE IDEOLOGY OF FIRE SUPPRESSION SYSTEMS.

Fire suppression systems is a broad field that contains many different engineered categories with different ideologies. They are all gathered to build a system to extinguish fires through various types of applications and substances and is difficult to define unless determining the type of hazard and its environment.

To choose the ideal fire suppression system for your needs depends on various factors. While all can suppress a fire, each system has its pros and cons, including various cost levels. A fire suppression expert is needed to select the correct solution.

A fire suppression system has components that combine to detect fires at the fire outbreak through warning signals such as heat, smoke, and other detection devices. These are attached to an alarm system that will alert at fire detection and initiate sequential and consecutive steps to suppress the fire. The fire suppression system will automatically release an external substance’s application to extinguish the fire after the detection alert. The fire suppression system also has a manual application to reduce the time between the alert stage and the external substance release to extinguish the fire.

FIRE SUPPRESSION SYSTEMS CLASSIFICATIONS

The halocarbon gases are extracted from the atmosphere and blended to use in clean agent systems. These gases work to extinguish the flames by absorbing so much heat from the flames that the flames become chemically unstable. They discharge within ten seconds into the hazard space and reach a concentration rich enough to extinguish the fire after another ten seconds. The Halocarbons gases have some familiar names:

Chemical Clean Agents FM-200 (HFC-227ea), ECARO-25 (HFC-125), FK-5-1-12 (3M Novec 1230) Fire Protection Fluid, and others. All of these types offer fast-acting fire-suppressing. Clean agents protect areas, such as computers, servers, electronics, artwork, archives, etc.  Compared with traditional water sprinkler systems, clean agent systems act faster and safer than water, limiting damage and downtime.

The quantity of halocarbon agent required to achieve the design concentration shall be calculated from the following equation NFPA 2001:

W = V/S (C / 100-C)

Inert gases include nitrogen, argon, and sometimes carbon dioxide, or a combination of two or more. Inert gases reduce oxygen concentration levels primarily to a point where combustion cannot be sustained and are safe for both people and the environment.

The reducing oxygen concentration in inert gas systems does not go below 12% oxygen inside the hazard area, giving people enough time during a discharge to exit safely. These systems have a more extended discharge time, around 60 to 120 seconds, and it has lower discharge pressure inside the hazard area to prevent causing a problem with room integrity.

Inert gases are highly cost compared to the halocarbon family of gases because inert gas systems have longer retention time and produce no fogging during discharge. Inert gas systems take up more floor space and more physical steel in the system. Because of more tanks and more valves than halocarbon systems.

X=2.303 x (S0/S) x log10 (100/100-c)

SAFETY AND DESIGN CONCERNS FOR CLEAN AGENT SYSTEMS

The engineering designers take room construction as the first element to achieve occupancy and equipment’s best protection levels. They measure and study the construction zone to ensure few leaks paths for the gas to escape quickly. Also, limiting leaks during the peak pressure wave of the gas discharging into the room and predicted hold time of clean agent discharge.

The peak pressure created in an enclosure depends on many factors: the agent concentration and discharge time, humidity, opening characteristics of the system discharge valve, and the aggregate vent area of the enclosure.

The most influential parameter is the aggregate vent area, which comprises all openings, whether unintentional or intentional.

Pressures are developed within an enclosure during the discharge of both inert and halocarbon clean agents.

The discharge of the inert agent results in only a positive pressure change

On the other hand, the discharge of a halocarbon agent usually creates an initially negative pressure change, followed by a positive pressure change.

These considerations mentioned earlier will help reduce the number of piping runs to nozzles, located at the ceiling of space, to arrange and distribute the gas systems into the hazard space. The system has an electrical component that must be considered, which is the releasing fire alarm system – it includes the control panel, detectors, notification devices, and the abort switch. To locate the agent cylinders inside the protected area that will achieve the lowest installation and piping cost for the systems. Suppose the hazard zone has area similarity with the same volume. In that case, that is the other to reduce the cost by using one bank of tanks with selector valves that directionally route that gas to whichever zone has the fire and requires the gas.

Engineers take the concentration for the systems as a serious safety concern. Because the clean agent systems are volumetrically designed and have a specific amount of agent for the volume, if the hazard area gets bigger and not putting the proper specific amount of gas, then it will not achieve that extinguishing concentration to suppressed the fire. And if the amount of concentration goes up to the specific amount of gas, then it will cause a problem for human safety.

The halocarbon agent and inert gases are considered to be the most environmentally friendly clean agent systems if it is appropriately designed.

KITCHEN FIRE SUPPRESSION SYSTEMS APPLICATIONS

All cities around the world has restaurants and clubs catering to their people. Numerous fast-food chain restaurants, food courts, hotels and stores. And where there is hot food preparation, there is the potential for fire. Modern cooking requires deep fat fryers, broilers and grills, and there is always the risk of severe fires. Until the mid-20th century kitchen fires were not uncommon and restaurants would burn to the ground before the flames could be contained and suppressed. This problem was not successfully addressed until 1962 – it was then that the manufactures and scientists in fire suppression introduced a system specifically for commercial kitchens that would automatically detect and suppress a fire in the cooking area. This initial effort was a major success and brought the restaurant safety to a new, acceptable level. But the fire suppression system engineers were not satisfied with this initial effort and wanted more improvement. Soon they introduced the wet chemical agent system with the formula K2CO3 that has become the industry standard for restaurant fire suppression around the world.

There are two system design options:

The primary is an appliance specific design where nozzles are aimed at specific hazard areas of the appliance, which is considered the most economical design because the agent is aimed only where it is needed.

The other option is overlapping appliance protection in this design scheme the nozzles are installed in a straight line and provide overlapping discharge patterns – using this layout appliances can be moved or replaced. As long as they stay within the fire-free zone, they will be protected.

In the event of a fire, the fusible link detection system responds rapidly to the growing heat, and when the temperature rating is exceeded, the fusible link separates. This triggers the release of a compressed gas cylinder (pre-filled with the extinguishing agent and charged with dry nitrogen to a pressure of 225 psi at a temperature of 70 F) within the release mechanism. Simultaneously, the compressed gas pressurizes and selects the agent tank and an air cylinder that trips the mechanical gas shutoff valve. The agent is then dispersed throughout the system, rapidly knocking down the flames – and because it has a neutral pH factor, it helps prevent fire reflash. The agent creates a foam blanket that inhibits the release of flammable vapors and cools. After system discharge, the valve assembly must be rebuilt to ensure proper future operation.

The hazard area, in certain instances, may be necessary to discharge the system manually by a remote manual pull station. This pull station is made out of a rigid red moulded composite material which makes it easier to recognize as the manual means for fire suppression system operation.

To provide maximum assurance for suppression systems that will operate effectively and safely must be performed according to the following codes:

NFPA 96 (Standard for the installation of equipment) and

NFPA 17A (Standard on Wet Chemical Extinguishing Systems)

AEROSOL FIRE-EXTINGUISHING SYSTEMS is a part of the fire suppression systems that can automatically operate and extinguished the fire within seconds, through removing the heat. This system used to protect hazards within specific limitations of applications and per their listing.

The aerosol is economical to fire extinguishing and easy to install, and generators after discharge are easy to resume within a short time as no pressure cylinders or piping is required.

Aerosol units consist of non-pressurized generators and contain a solid compound that, when activated, produces an ultrafine cloud of condensed aerosol that chemically extinguishes fire without any harmful effects.

These units are sealed in stainless steel canisters and wired to a control panel mounted to walls and mechanical heat-detecting actuators are also positioned inside electrical cabinets for localized fire protection, visual and audible alarms and smoke detector, these smoke detector is attached to a fire alarm control panel.

When a small fire starts inside the electrical cabinets, the smoke will release into the room and quickly be detected by the aspirating smoke detector which signals to the control panel and triggers the horn and stroke as the fire continues to grow. Several continents units in each of the cabinets are then actuated. Thermal switches are triggered, sending a signal to the control panel which initiates full room fire suppression. A second horn and strobe go off giving a 30-second warning of a total flooding event – all the wall-mounted units discharged into the room the aerosol clouds remain active to reduce the risk of flashover or re-ignition.  After 10 minutes, the room is vented out, leaving little residue and no toxic or harmful.

DESIGN CONCERNS FOR AEROSOL SYSTEMS

In the design of a total flooding system, the integrity of the protected enclosure must be considered, and to prevent loss of agent through openings to adjacent hazards or work areas; openings must be permanently sealed or equipped with automatic closures.

Forced-air ventilating systems must be shut down or closed automatically where their continued operation would adversely affect the performance of the fire-extinguishing system or result in the propagation of the fire.

The volume of the ventilation system and associated ductwork must be considered part of the total hazard volume when determining the quantity of the agent.

The protected enclosure must have the structural strength and integrity necessary to contain the agent discharge.

If the developed pressures present a threat to the structural strength of the enclosure, venting shall be provided to prevent excessive pressures.

To determine the Quantity or The mass of an aerosol-forming compound required, calculated from the following formula:

m = da x fa x V

Aerosol fire-extinguishing systems can be used in Marine Systems to protect hazards that are partially or enclosed or equipment that is partially or enclosed on vessels  with specific Design requirements.

Health Effects.

Are these systems safe? To determine the health effect of using this system in spaces that are occupied or unoccupied, it depends on the evaluation of the potential adverse health effect from the engineering sides by assessed for the density, size of the particulates. And the concentration of gases expected after actuation of the aerosol extinguishing system at the design application density.

For Marine Systems

In these specific applications, the particles of the powdered aerosol fire suppressants must be 10 µm for maximum effectiveness. This size of Particles can be inhaled and can give potential exposure to the respiratory system. For humans size 5 µm to 30 µm of these particles can be deposited in the nose and throat region (nasopharyngeal). Powdered aerosols are typically composed of multiple soluble and insoluble compounds. As such, acute inhalation exposure to very high concentrations of these compounds can induce a variety of adverse effects in humans. Therefore, a limited battery of toxicity tests is required to determine the appropriateness of the powdered aerosol system for use in occupied spaces.

Aerosol Potential Effect on Visibility

The visibility is an essential factor to escape a fire hazard when powdered aerosols fire extinguishers are used for occupied spaces. It is essential to have data on the aerodynamic properties of the powdered aerosol, and that is the mass median aerodynamic diameter (MMAD), These values are necessary to determine where the particles can deposit within the airways of a rodent model and in a potentially exposed to a human.

To ensure that powdered-aerosol products will meet the visibility requirements of the appropriate organizations, several methods and models based on the standard visual range formula and Mie theory.

Lv = 1200/c

Or Calculations resulting from the Mie scattering visibility model

That indicates visibility of 1 m or more can be achieved by increasing the MMAD particle size

Aerosol systems must be performed per NFPA 2001 (Standard on CLEAN AGENT FIRE EXTINGUISHING SYSTEMS) and All wiring systems shall be installed per NFPA 72.

Carbon Dioxide (CO2) FIRE SUPPRESSION SYSTEMS Provide large presentations of concentration gas that reduces the oxygen level to a point where combustion cannot occur. CO2 Systems is unsafe for people. The CO2 system will extinguish fires in Class A, B, and C hazards, and are only recommended for localized applications or areas generally inaccessible by employees or customers.

CO2 is a colourless, non-electrical conductive and odourless gas that does not leave any residue after discharge. This means there is no damage to the equipment placed in the protected space.

The CO2 system consists of a cylinder (container of the gas quantity pressurized with 3000 psi) with valve assembly. The valve opens automatically when the actuation pressure reaches 100 to 110 psi.

Head Valve with solenoid valve can be used as the head of Master Cylinder Head Valve. The head valve can be actuated by two methods of operation, Electric (solenoid actuator) or Manual ( Mechanical actuator). The cylinder has connected the pipe network through flexible hose connections and the discharge nozzle attached directly to the pipe network.

These mechanical components of the CO2 system come with an alarm system and detection devices attached to a fire control panel. When the fire initiates, the smoke and heat detector devices will transfer a signal to the control panel that there is a fire. The solenoid then automatically opens and release the agent to suppress the fire – as well as the pressure switch, which activates the audible and visual devices.

The CO2 Systems can either be used in a Local Application System or a Total Flooding System.

Local Application System. A system consisting of a supply of extinguishing agent arranged to discharge directly on the burning material and surface fires in flammable liquids in non-enclosable areas or where the enclosure does not conform to the requirements for total flooding.

Total Flooding System. A system consisting of a supply of carbon dioxide arranged to discharge into and fill to the proper concentration, an enclosed space, or enclosure around the hazard.

Common areas where CO2 fire suppression systems installed include electrical hazards, record (bulk paper) storage, ducts, covered trenches, fur storage vaults, dust collectors, combustible materials area.

The design based on volume consideration with specific flooding factors for each space and the minimum design CO2 concentration can be different between hazards and must be compatible with NFPA 12

SAFETY AND DESIGN CONCERNS FOR CO2 FIRE SUPPRESSION SYSTEM

CO2 can cause asphyxiation in humans if the concentration reaches 7.5%, that’s why the systems are designed to have a pneumatic siren that warns people to exit hazard areas where the CO2 will be discharged from the suppression system. The pneumatic siren is one of the life safety devices.

CO2 Systems are dangerous. It is essential for people around the hazard protected by CO2 Total Flooding System to be trained on the dangers of this system and how to evacuate safely if the system is preparing to discharge and suppress the fire.

The CO2 concentration, in most cases, are designed to be 34%, but it can be more dangers, when it’s used to protect areas such dry electrical hazards 50%, Record (bulk paper) storage, ducts, covered trenches 65%, and Fur storage vaults, dust collectors 75% as a minimum design CO2 Concentration.

WATER MIST FIRE SUPPRESSION SYSTEMS

Water mist systems are a fixed fire protection system that automatically uses water to suppress or extinguish a fire by producing ultra-fine water droplets. It used 50 to 90% less water than a traditional fire sprinkler. Water mist systems may be connected to a building’s water supply for continuous fire-fighting capability, or in remote locations, may be connected to a tank or reservoir.

Water mist systems help provide effective cooling and fire control on Class A fires, or assistance with extinguishing and preventing re-ignition on Class B or Class F fires.

The system consists of automatic nozzles with a heat-sensitive quick response glass bulb attached to a piping system and connected to a water supply that’s used to actuate the water. In the event of a fire, the nozzles discharge a cone of spray containing small water droplets that fill the protected zone with water mist.

The Water Mist Systems can be installed as

Wet Pipe Water Mist System. A water mist system using automatic nozzles attached to a piping system containing water and connected to a water supply so that water discharges immediately from nozzles operated by the heat from a fire.

Dry Pipe Water Mist System. A water mist system using automatic nozzles attached to a piping system containing air, nitrogen, or inert gas under pressure, the release of which (as from an opening of an automatic nozzle) allows the water pressure to open a dry pipe valve. The water then flows into the piping system and out through any open nozzles.

Pre-action Water Mist System. A water mist system using automatic nozzles attached to a piping system that contains air that might or might not be under pressure, with a supplemental detection system installed in the same areas as the mist nozzles. The actuation of the detection system opens a valve that allows water to flow into the piping system and discharges through all opened nozzles in the system.

Deluge Water Mist System. A water mist system utilizing non-automatic mist nozzles (open) attached to a piping network connected to the fluid supplies through a valve controlled by an independent detection system installed in the same area as the mist nozzles.

Local-Application Water Mist System. A water mist system is arranged to discharge directly on an object or hazard in an enclosed, unenclosed, or open outdoor condition.

Water Mist Droplet Size Characterization and Measurement

Most successful use of water mist fire protection systems is the increased surface area per unit water volume afforded with the generation and application of small droplets. The increased surface area dramatically increases the rate of heat transfer from the fire to the water mist droplet, cooling the combustion reaction and diluting the oxygen concentration with the generation of water vapour in the vicinity of the fire. It is important to characterize the droplet size distribution produced in listed nozzles for use in the future design and application of water mist systems. It will be valuable in assessing the ability of water mist droplets to control, suppress, and extinguish fires of all types and sizes.

For Low-Pressure System The Hydraulic calculations for water mist systems with working pressures not exceeding 12 bar (175 psi) and having no additives shall be permitted to be performed using the Hazen–Williams calculation method.

High-Pressure System. A water mist system where the distribution system piping is exposed to pressures of 34.5 bar (500 psi) or greater.

Intermediate Pressure System. A water mist system where the distribution system piping is exposed to pressures greater than 12.1 bar (175 psi) but less than 34.5 bar (500 psi).

Low-Pressure System. A water mist system where the distribution piping is exposed to pressures of 12.1 bar (175 psi) or

The Pressure Loss in Intermediate and High-Pressure Systems

NFPA750 Standard on Water Mist Fire Protection Systems

FOAM EXTINGUISHING SYSTEMS Are commonly use for pro­tecting high-risk areas, particularly in the fire categories A and B, and mostly used for flammable liquids and combustible liquids in tanks or processing areas to prevent or extinguish fires by excluding air and cooling the fuel. The foam system is, either low expansion foam or medium-high expansion foam systems.

The foam fire suppression is a foam concentrate AFFF, water, and air. When these three ingredients are mixed, these can create a foam solution and forming air-filled bubbles formed from aqueous solutions with lower density than the lightest flammable liquids.

Foam concentrates protein foam concentrate diluted with water to form 3% to 6% solutions, only used for crude oil fires.

Fluoroprotein foam concentrate is similar to protein foam concentrates diluted with water to form 3% to 6% solutions and deposit vaporization preventing film on the surface of liquid fuel. It is used for crude oil or refined oil products where a higher degree of protection is preferred.

Aqueous film-forming foams AFFF concentrates used to produce foam to solution volume ratios from 20:1 to 1000:1 and are used for local protection and engine room.

FOAM SYSTEM CLASSIFICATIONS:

Low expansion foam. Small foam bubbles discharged through sprinkler systems, fire hoses, monitors, spray nozzles, and foam makers. Used for flammable liquid storage, fuel storage tanks.

Medium Expansion Systems are primarily used for vapour suppression in refineries and chemical manufacturing areas.

High Expansion Systems Large foam bubbles, preferred for total flooding of a hazard area or large area volume protection is needed. The most common applications used for aircraft hangars, total flooding warehouses, and Liquefied Natural Gas dock.

Foam systems components

System Tanks can be pre-piped vertical or horizontal and Foam pump skids.

Proportioning Devices releases the proper amount of concentrate into the water supply based on the solution required.

Discharge Devices

Foam discharge devices. Can be water sprinkler nozzles compatible with foams, monitors, foam makers, handline nozzles, and High expansion foam generator.

The piping network connecting the foam discharge devices to the System Tanks.

Alarm systems with detection devices (thermal detectors or quick-response flame detectors), sounding alarms, and electric control panel.

The foam fire suppression systems, in the event of a fire the detection devices will signal the control panel, the valves will open. The foam systems will be actuated to flow the water into the piping system, and the proportioning devices inject the foam concentrate into the water. These will generate foam solution discharging through the discharge devices to suppress the fire by separating the liquid fuel from the air.

Calculation

The minimum rate of discharge or total generator capacity shall be calculated from the following formula:

R = (V/T+Rs) x CN x CL

R= S x Q

Expanded foam velocity also can be calculated by using the following formulas:

Velocity (ft/sec) = Expanded foam (gpm)/KA

Foam systems must be performed per

NFPA 11 (Standard for Low-, Medium-, and High-Expansion Foam) and

NFPA 1050 (Foam Chemicals for Fires in Class A Fuels).

THE WATER AS FIRE EXTINGUISHING AGEN, THAT KNOWN AS SPRINKLERED SYSTEMS

This type of system can perform well to extinguish the fire. The system discharges the water with specific density in area occupancies that have light, ordinary and extra hazards. It can be used in a wide range of facility depending on the hazard classifications.

The system consists of a head discharge sprinkler with rated temperature indicated by colour coding for its glass bulb and detriment by sprinkler k-factor based on ceiling height.

Water pumps to deliver the water from tanks into the sprinkler’s head through the piping network.

The Piping network, either pressurized water or nitrogen and controlled by gate valves.

Type of Sprinkler Systems

Wet sprinkler systems – the sprinkler attached to a piping network contains pressurized water. When a fire ignites, the heat will rise to break the glass bulb of sprinklers due to thermal expansion for the mercury inside the bulb and the water immediately discharge to extinguish the fire before it spreads.

Dry sprinkler systems – the sprinkler attached to a piping network contain pressurized air or nitrogen. When a fire ignites, the sprinkler will open and the air release to decrease the pressurized water at the dry valve, and it will open to flow the water into the fire hazard.

Pre-action Sprinkler systems – the sprinkler attached to a piping network contains air, either pressurized or not pressurized. The system is attached to the detection system when a fire ignites, and the detection system will be activated and signal the control panel to open the valve. The water will flow to extinguish and stop the fire from spreading.

Deluge Sprinkler system sprinklers with an open head attached to a piping network and the valves are opened by the operation detection system. When the system activated, the water will discharge from all sprinklers attached to the system.

Water sprinkler systems must be performed per:

NFPA 13 (Standard for the Installation of Sprinkler Systems).

NFPA 13D (Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes).

NFPA 13R (Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies).

NFPA 20 (Standard for the Installation of Stationary Pumps for Fire Protection).

In conclusion, to successfully extinguish or suppress fires, you have to apply as follows:

Passive fire protection:

An architecture engineering methodology that divides the building and facility into separate sections and prevents the spread of fire through the use of fire-resistance-rated walls and floors. Using fire doors to help these separated sections of the structure and to prevent the spread of fire and smoke throughout the ducts of the building. Or to use multiple floors is path markers. These markers assist in the evacuation process by lighting the way through the dark in case of fire spreading.

Active fire protection:

A methodology which intends to suffocate the oxygen, restricting the fire and cooling down the fire.

Suffocating the oxygen by using gas or foam systems.

Restrict the fire to cut fuel supply or remove combustible materials.

Cooling down the fire is to using water systems.